The present invention relates in general to fluid-operated oil well pumping systems of the type wherein a pump unit which includes a fluid operated pump is circulated into and out of its operating position in a well. More particularly, the invention relates to an open system wherein the production fluid discharged by the pump and the spent operating fluid discharged thereby are mixed together and conducted to the surface through a common, production tubing. Operating fluid under pressure for actuating the fluid operated pump is delivered thereto through a parallel supply conduit, or through the annulus between the well casing and the production tubing.
Still more specifically, the present invention contemplates a fluid operated pump system which is of the reverse circulation type wherein the pump is circulated into and out of the well through a production tubing which is relatively large, and wherein the operating fluid is delivered to the pump through a parallel supply tubing which is relatively small or through the annulus between the well casing and the production tubing. Such a reverse circulation system has the advantage of minimizing fluid friction since the combined flow of production fluid and spent operating fluid is conducted to the surface through the larger production tubing, the smaller flow of operating fluid under pressure being conducted downwardly to the pump through the smaller supply tubing or through the annulus.
With such a reverse circulation system, prior art pump units are normally run in by introducing fluid under pressure into the production tubing thereabove, and the pump unit is circulated out by introducing fluid under pressure there beneath through the return conduit. Since the supply conduit contains operating fluid under high pressure during normal operation of the fluid operated pump when the pump unit is in its housing at the lower end of the production tubing, latch means are provided for preventing upward circulation of the pump unit through the production tubing of the pump unit during normal operation of the fluid operated pump.
Prior art attempts to improve upon fluid operated pump systems of the reverse circulation type have always seemed to require the use of a complicated latch means. U.S. Pat. No. 2,869,470, granted Jan. 20, 1959 to Clarence J. Coberly, is exemplary of patents disclosing latch means for latching the pump unit in its operating position against the upward bias resulting from the application of the operating fluid under pressure in the supply tubing to the lower end of the pump unit. After the pump unit arrives in its operating position in the housing at the lower end of the production tubing, the latch means is set by gradually building up the operating fluid pressure in the supply conduit, frictional resistance being sufficient to prevent upward displacement of the pump unit before the latch means is set as long as the operating fluid pressure is increased slowly. When it is desired to circulate the pump unit out through the production tubing, the latch means is released by increasing the pressure in the production tubing. The Coberly pump unit can be latched and unlatched hydraulically by selective pressure applications to the latch means. However, malfunctioning of the hydraulically operated latch means makes it extremely difficult to set or release the pump unit. If the pump unit cannot be latched in its operating position, it must be circulated out and repaired or replaced. On the other hand, if the latch means cannot be released, due to the effects of corrosion, sand accumulations, or the like, it may be necessary to pull the entire tubing system.
U.S. Pat. No. 3,687,573, granted Aug. 29, 1972 to Ralph F. McArthur, et al is an example of prior art attempts to provide a mechanically actuated latch means as opposed to the Coberly hydraulically actuated latch means.